Douglas Rathgeb made a point of this in the commentary for the movie, and I had thought about it a little prior to hearing him talk about it, but really, you gotta wonder, WHAT happened with Jim's grandma? She was there at the police station, she was at the house bright and early the next morning, and then she was just gone with no explanation. Why?
sharedidn't the movie mostly occur on the first day of school? Perhaps grandma lives somewhere else (reaching here). Plus she wouldn't have gotten up in the middle of the night to look for Jim. She's old and need her old-people rest. Best answer I can think of is that she croaked in the afternoon and the b!tch mom made the dad sweep her under the rug.
shareMy guess is she didn't live with Jim's parents and had plenty of money to live comfortably, and just came over to aggravate his mother and sympathize with Jim and his father.
MM